Microfluidic delivery devices are commercially available for delivering very small amounts of fluid. It is common for microfluidic delivery devices to employ one or more valves that may be formed on or within the device. Microfluidic valves can be made using micro-electro-mechanical systems (MEMS) manufacturing techniques to form a MEMS device. Such MEMS devices may include one or more valves and other features for controlling fluid flow. Microfluidic valves are used typically with a microfluidic pump and are useful for delivering drug fluids, such as insulin, and small quantities of other fluids.
One example of a conventional microfluidic valve structure 110 formed in a MEMS device is illustrated in FIGS. 1-3. The conventional microfluidic valve structure 110 is generally formed in a body having a substrate 112, such as a silicon substrate, using conventional MEMS fabrication processes. Essentially, one or more layers of silicon are etched away to form a fluid passage and valve components for controlling the flow of fluid through the passage. As seen, a passage 122 is formed extending through the valve body including substrate 112 and has an inlet 121 and an outlet 120. A valve boss 124 is suspended via three radial support arms 130A-130C adjacent to a valve seat 126. The valve boss 124 is positioned above the fluid passage 122 and is capable of moving up and out of contact with seat 126 and down and into contact with seat 126 therethrough to open and close the fluid passage 122 to allow fluid to flow in path 128 or prevent fluid flow. As shown in FIG. 2, fluid flows through microvalve structure 110 through passage 122 and around the valve boss 124 and exits outlet 120. The valve boss 124 shown is normally open to allow fluid to flow through the passage 122. When the fluid path is reversed, the valve boss 124 is forced into position against the seat 126 via back pressure to prevent fluid flow therethrough. Thus, the valve structure 110 operates as a one-way check valve.
Some valve bosses used in microfluidic devices are attached to the rim of a flow channel, shown here as outlet 120, by tethers or springs 130A, 130B and 130C that extend radially from the boss 124 as shown. Such valves may be displaced out of plane when the valve 110 is placed under stress, particularly if the stress on the valve is a compressive force F as shown in FIG. 3. Tensile stresses tend to increase the force needed to actuate the valve boss 124, and may also keep the valve boss 124 from properly closing. Under stress, the valve boss 124 may not seat properly upon the valve seat 126. This may lead to a leaky valve or inefficient device.
Many conventional valve designs employ three support arms (tethers) spaced at one hundred twenty degrees (120°) from each other extending radially from the valve boss to the wall of the outlet channel. These types of conventional valves may be prone to out-of-plane (cross-axis) movement under stress or when actuated. This may prevent a good seal between the valve boss and the seat, thereby resulting in a leaky valve and inefficient device.
It is therefore desirable to provide for a microfluidic valve structure that provides a good seal between the valve boss and the seat, to prevent leakage or inefficiency in the device. Additionally, it is desirable to provide for a valve structure that is generally immune to out-of-plane movement under stress or when otherwise actuated.